1. Field of The Invention
The present invention relates to a magnetoresistant reading and optionally writing magnetic head for longitudinal recording and a process for producing such a head.
2. Discussion of The Background
The structure of a reading and a writing head for longitudinal recording is shown in FIG. 1. In a semiconductor substrate 10 are deposited and etched various layers (whose relative dimensions have not been respected for reasons of clarity) in order to form a magnetic circuit 12 with an air gap filled by an amagnetic spacer 14 and a conductor coil 16. The track to be written and/or read 20 passes above the air gap. Such heads are described in various different embodiments in European Patents 152 326 and 262 028 (or the corresponding U.S. Pat. No. 4 837 924).
Alongside this known thin film technology has developed a method using the properties of magnetoresistant materials. Such materials make it possible to produce reading heads for very narrow recording tracks.
FIG. 2 shows a head of this type comprising a magnetic support 1 coated with an insulating layer 2, a magnetoresistant layer 5 located beneath a slot 6 made in a magnetic layer 7. The latter is in contact with the support 1 by a rear zone 8. Therefore the layers 1,7 and 8 form a magnetic circuit with air gap 9, the circuit being interrupted by the slot 6. When a recorded track passes in front of the air gap 9, the magnetic flux detected level with the air gap in part passes through the magnetoresistor 5, which undergoes a resistance modification. Such a head is described in U.S. Pat. No. 4 703 378.
FIG. 3 shows another known head using magnetoresistors. A semiconductor support 30 has been deposited on a magnetic circuit 32 with a spacer 34. Two slots 36,37 interrupt the magnetic circuit and serve to house two magnetoresistors 38,39. Such a head is described in European Patent 284 495.
All magnetoresistance devices operating according to a general principle can be illustrated by FIGS. 4,5 and 6.
FIG. 4 shows a magnetoresistor 40 having a magnetization vector M, which, under the effect of an external magnetic field Hext, rotates by an angle .alpha.. Therefore the resistance of the element 40 is modified. This resistance can be electrically measured through two connections 42,43. The resistance variation .DELTA.R, related to the resistance R, varies in the manner indicated in FIG. 5 as a function of the angle .alpha.. In practice, for a 0.1 .mu.m thick iron-nickel layer, the relative resistance varies by approximately 1% when the magnetization turns by 90.degree..
In order to increase the sensitivity of the measurement and improve the linearity, the magnetization of the layer is oriented to 45.degree. so as to be able to work on the edge of the curve, in the manner shown in FIG. 6. Thus, a larger .DELTA.R is obtained for the same .DELTA.H, the magnetization M rotating with respect to the direction by 45.degree..
Although the prior art devices are satisfactory in certain respects, they still suffer from certain disadvantages. In particular, they have a complex construction, particularly when it is a question of placing the magnetoresistor beneath or in the magnetic circuit slot.